Workplace for Measuring of Thermomechanical Loading

Práce se zaměřuje na problematiku termomechanického namáhání, na spolehlivost eletrotechnických sestav, na poruchy pájeného spoje a bezolovnaté pájecí slitiny. Cílem práce je návrh a realizace pracoviště pro měření termomechanického namáhání.The work is focused on problematic of thermomechanical tensions, reliability of electrotechnical assemblys, failures of solder joints and lead-free soldering alloys. The goal of work is project and realisation of station for measuring thermomechanical loading.

New insight on south western iberian rock art by non-invasive analytical approaches: the cases of Ardales and Escoural Cave

This thesis focuses on Escoural Cave, in southwestern Iberia, known as the only cave within Portugal to contain Palaeolithic rock art. Estimated to be roughly 20,000 years old, the paintings and engravings found inside the hypogeal environment face possible degradation due to natural and anthropogenic factors. Although previously well documented, the importance of continuous monitoring and documentation of at-risk cultural heritage, specifically rock art, is important for its survival and for the implementation of future conservation efforts. One aim of this thesis was to use non-invasive techniques and methods to document and analyze the rock art at Escoural Cave. Various imaging techniques were used to further reveal parts of the hidden rock art found within Escoural Cave while also documenting the current state of preservation of the eight most well-known paintings. The work completed for this thesis also investigated the effectiveness and reliability of Vis-NIR FORS and hyperspectral imaging in their usefulness and applicability for non-invasive rock art research. The Vis-NIR FORS and hyperspectral camera were determined to be periodically useful for the work completed at Escoural Cave; many factors from, lighting, location of the rock art, and extensive amounts of calcite coverage over the paintings created non-ideal conditions within the cave for the complete effectiveness of these approaches. These methods were useful for non-invasive pigment identification and proved less reliable for the interpretation of possible organic binders. Lastly, the eight locations sampled throughout Escoural Cave for microbial growth showed - through the use of culture-dependent and the culture-independent method of NGS - that the majority of microorganisms in Escoural Cave are naturally found within karstic systems. However, the presence of some strains of Enterobacter sp. raises concerns as it can be pathogenic to visitors with compromised immune systems; additionally, the presence of lampenflora is of concern for the protection of the rock art and is a contender for future preventive conservation efforts through its removal; Resumo: Um novo olhar sobre a arte rupestre ibérica do sudoeste por adordagens analíticas não invasivas – os casos das grutas de Ardales e Escoural Esta tese centra-se na gruta do Escoural, no sudoeste da península Ibérica, conhecida como a única com arte rupestre Paleolítica, em Portugal. Estima-se que tenham cerca de 20.000 anos de idade, as pinturas e gravuras encontradas na gruta e enfrentam uma possível degradação devido a fatores naturais e antropogénicos. Embora previamente bem documentada, a importância do acompanhamento contínuo e da documentação do património cultural em risco, especificamente a arte rupestre, é importante para a sua sobrevivência e para a implementação de futuros esforços de conservação. Um dos objetivos desta tese foi usar técnicas e métodos não invasivos para documentar e analisar a arte rupestre da gruta do Escoural. Usaram-se várias técnicas de imagem para revelar ainda mais partes da arte escondida na rocha, no interior da gruta, permitindo também documentar o estado atual de preservação das oito pinturas mais conhecidas. Este trabalho também permitiu avaliar a eficácia e a aplicabilidade de FORS Vis-NIR e imagem híper-espectral como metodologias não invasiva em arte rupestre, revelando-se metodologias úteis para o trabalho desenvolvido nesta gruta; muitos fatores, iluminação, localização da arte rochosa, e extensas quantidades de cobertura de calcite sobre as pinturas criaram condições não-ideais dentro da gruta para a completa eficácia destas abordagens. Estes métodos foram úteis para a identificação não invasiva de pigmentos e revelaram-se menos eficazes para a interpretação de possíveis aglutinantes orgânicos. Finalmente, os oito locais amostrados para o crescimento microbiano mostraram-através do uso de cultura-dependente e do método cultura - independente de NGS-que a maioria do microrgnismos na gruta Escoural são naturalmente encontrados em ambientes hipogénicos. No entanto, a presença de algumas estirpes, por exemplo de Enterobacter sp. podem apresentar patogenicidade para os visitantes com sistemas imunológicos comprometidos; além disso, a presença de lampenflora é uma preocupação para a proteção da arte rupestre e é um candidato para futuros esforços de conservação preventiva através de sua remoção

Ultrafast photocurrents at the surface of the three-dimensional topological insulator Bi2Se3\mathrm{Bi}_2\mathrm{Se}_3

Topological insulators constitute a new and fascinating class of matter with insulating bulk yet metallic surfaces that host highly mobile charge carriers with spin-momentum locking. Remarkably, the direction and magnitude of surface currents can be controlled with tailored light beams, but the underlying mechanisms are not yet well understood. To directly resolve the "birth" of such photocurrents we need to boost the time resolution to the scale of elementary scattering events ($\sim$ 10 fs). Here, we excite and measure photocurrents in the three-dimensional model topological insulator $\mathrm{Bi}_2\mathrm{Se}_3$ with a time resolution as short as 20 fs by sampling the concomitantly emitted broadband THz electromagnetic field from 1 to 40 THz. Remarkably, the ultrafast surface current response is dominated by a charge transfer along the Se-Bi bonds. In contrast, photon-helicity-dependent photocurrents are found to have orders of magnitude smaller magnitude than expected from generation scenarios based on asymmetric depopulation of the Dirac cone. Our findings are also of direct relevance for optoelectronic devices based on topological-insulator surface currents

Singular robust room-temperature spin response from topological Dirac fermions

Topological insulators are a class of solids in which the nontrivial inverted bulk band structure gives rise to metallic surface states that are robust against impurity scattering. In three-dimensional (3D) topological insulators, however, the surface Dirac fermions intermix with the conducting bulk, thereby complicating access to the low energy (Dirac point) charge transport or magnetic response. Here we use differential magnetometry to probe spin rotation in the 3D topological material family (Bi$_2$Se$_3$, Bi$_2$Te$_3$, and Sb$_2$Te$_3$). We report a paramagnetic singularity in the magnetic susceptibility at low magnetic fields which persists up to room temperature, and which we demonstrate to arise from the surfaces of the samples. The singularity is universal to the entire family, largely independent of the bulk carrier density, and consistent with the existence of electronic states near the spin-degenerate Dirac point of the 2D helical metal. The exceptional thermal stability of the signal points to an intrinsic surface cooling process, likely of thermoelectric origin, and establishes a sustainable platform for the singular field-tunable Dirac spin response.Comment: 20 pages, 14 figure

The Proportional Odds Model for Assessing Rater Agreement with Multiple Modalities

In this paper, we develop a model for evaluating an ordinal rating systems where we assume that the true underlying disease state is continuous in nature. Our approach in motivated by a dataset with 35 microscopic slides with 35 representative duct lesions of the pancreas. Each of the slides was evaluated by eight raters using two novel rating systems (PanIN illustrations and PanIN nomenclature),where each rater used each systems to rate the slide with slide identity masked between evaluations. We find that the two methods perform equally well but that differentiation of higher grade lesions is more consistent across raters than differentiation across raters for lower grade lesions. A proportional odds model is assumed, which allows us to estimate rater-specific thresholds for comparing agreement. In this situation where we have two methods of rating, we can determine whether the two methods have the same thresholds and whether or not raters perform equivalently across methods. Unlike some other model-based approaches for measuring agreement, we focus on the interpretation of the model parameters and their scientific relevance. We compare posterior estimates of rater-specific parameters across raters to see if they are implementing the intended rating system in the same manner. Estimated standard deviation distributions are used to make inferences as to whether raters are consistent and whether there are differences in rating behaviors in the two rating systems under comparison

Design of Tools for Machining Plastics and Composite Materials

Bakalářská práce se zabývá návrhem nebo doporučením vhodných obráběcích nástrojů pro obrábění především kompozitních materiálů. Teoretická část je věnována charakteristice materiálů a problematice obrábění úzce spojené s použitým materiálem v experimentu. Praktická část je zaměřena na porovnání fréz vhodných pro obrábění kompozitních materiálů na základě hodnot řezných sil a drsností získaných při experimentu. Veškeré údaje byly zpracovány a výsledná doporučení jsou uvedena v závěru.The bachelor's thesis deals with the design or recommendation of suitable machining tools for machining mainly composite materials. The theoretical part is devoted to the characteristics of materials and the issue of machining closely related to the material used in the experiment. The practical part is focused on the comparison of cutters suitable for machining composite materials based on the values of cutting forces and roughness obtained in the experiment. All data were processed and the resulting recommendations are given in the conclusion.346 - Katedra obrábění, montáže a strojírenské metrologievýborn